A light-emission procedure of an organic electroluminescence device is just an energy transfer procedure, in which electric energy is converted into optical energy. During this conversion, the organic electroluminescence device may be deemed as an injection-type light-emitting diode (LED). In the case that a voltage is applied to two ends of the organic electroluminescence device, under the effect of an electric field generated due to the applied voltage, electrons may be injected from a cathode of the organic electroluminescence device to an electron transport layer and holes may be injected from an anode of the organic electroluminescence device into a hole transport layer. These two carriers enter a light-emitting layer and are combined into excitons which are capable of emitting light through radiative recombination.
Usually, metallic electrodes are widely used in an organic light-emitting diode (OLED) device, and surface plasmon (SP) is generated at a metallic surface. To be specific, the movement of the electrons in a lateral direction (a direction perpendicular to a metallic surface) at the metallic surface is obstructed by the surface, and concentrations of the electrons in proximity to the surface are distributed gradiently, so plasma oscillation is formed in such a manner as to be restricted to the metallic surface. This electron dilatational wave formed by the plasma oscillation on the metallic surface is defined as the SP. The SP is propagated in a direction along an interface between a metal and an organic material, and an electric field intensity is decreased exponentially in a direction perpendicular to the interface. The SP is capable of being coupled with the excitons so as to generate exciton annihilation, so photons generated by an electro-luminescence (EL) material cannot leave the device, and instead, they may be absorbed by the metal in the form of SP oscillation localization or lost in the form of heat. In this regard, the external quantum efficiency of the EL device may be remarkably reduced.
Due to the fraction of power coupled to SP and the excitons at the interface between the metal and the EL material, luminous efficiency of the EL device may be remarkably reduced. For the OLED device, especially a bottom-emission device, due to the coupling of the SP with the excitons, a considerable optical loss may occur.